Curved interface between an outer end of a wing and a moveable wing tip device

ABSTRACT

An aircraft (1002) including a wing (1001), having a fixed wing (1005) with a wing tip device (1003) moveably mounted at the outer end thereof. The wing tip device (1003) is moveable between: a flight configuration; and a ground configuration about an axis of rotation. The wing tip device (1003) and the fixed wing (1005) meet along an interfacing cut line (1035). The interfacing cut line (1035) includes a curved section (1039) cent red on the axis of rotation (1011), the radius of the curved section constantly increasing as the cut line passes around the axis (for example a spiral shape).

RELATED APPLICATION

This application claims priority to United Kingdom (GB) PatentApplication 1719640.3 filed Nov. 27, 2017, the entirety of which isincorporated by reference.

BACKGROUND OF THE INVENTION

There is a trend towards increasingly large passenger aircraft, forwhich it is desirable to have correspondingly large wing spans. However,the maximum aircraft span is effectively limited by airport operatingrules which govern various clearances required when manoeuvring aroundthe airport (such as the span and/or ground clearance required for gateentry and safe taxiway usage).

To address this problem, various arrangements comprising moveable wingtip devices, that specifically enable the span to be reduced in a groundconfiguration, have been suggested.

WO2015/150835 is an example of a suggested arrangement. In thearrangement of WO2015/150835 the wing tip device and the fixed wing areseparated along an oblique cut plane and the wing tip device isrotatable about an axis of rotation perpendicular to that cut plane.

In the arrangement of WO2015/150835, sealing the interface between thefixed wing and the wing tip device (when the wing tip device is in theflight configuration) has been found to be problematic. Morespecifically, as the wing tip device rotates between the flight and theground configurations, relative sliding motion occurs at the interfacebetween the outer end of the fixed wing and the inner end of the wingtip device. Whilst a sliding seal may, in principle, be employed, such asolution is sub-optimal because sliding seals tend to be subjected torelatively large amounts of wear. This may make them susceptible to wearand/or damage and may therefore necessitate frequent inspection and/orreplacement of the seal.

UK patent application GB1610108.1 in the name of Airbus OperationsLimited (filed on 9 Jun. 2016, and currently unpublished) suggests anarrangement in which the outer end of the fixed wing and the inner endof the wing tip device meet along an interfacing cut line that separatesthe outer surfaces of the fixed wing and the wing tip device. Thecontents of GB1610108.1 are incorporated herein by reference. In anembodiment described in GB1610108.1, the interfacing cut line comprises:a first length, formed by a cut through the outer surface, but offsetfrom the primary cut plane in a first direction; a second length, formedby a cut through the outer surface but offset from the primary cut planein a second direction, opposite to the first direction; and a transitionsection over which the interfacing cut line transitions from the firstlength to the second length. The wing tip device may contact the fixedwing at a sliding contact along the transition section, but the wing tipdevice separates away from the fixed wing along the first length andsecond lengths. In GB 1610108.1, the transition section may be a numberof possible shapes.

Aspects of the present invention seek to provide yet furtherimprovements to the interface between the fixed wing and the wing tipdevice.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided anaircraft comprising a wing, the wing having a fixed wing with a wing tipdevice moveably mounted at the outer end thereof, the wing tip devicebeing moveable between: (a) a flight configuration for use duringflight; and (b) a ground configuration for use during ground-basedoperations, in which ground configuration the wing tip device is rotatedaway from the flight configuration about an axis of rotation such thatthe span of the aircraft wing is reduced. When the wing tip device is inthe flight configuration, the outer end of the fixed wing and the innerend of the wing tip device meet along an interfacing cut line thatseparates the outer surfaces of the fixed wing and the wing tip device.The interfacing cut line comprising a curved section centred on the axisof rotation, the radius of the curved section continuously increasing asthe cut line passes around the axis.

Providing an interface having a curved section in which the radius ofthe curved section continuously increases around the axis of rotation,has been found to be especially beneficial. In particular, since theradius of the curved section of the interfacing cut line increases, andthat curved section of the interfacing cut line is centred on therotational axis of the wing tip, it means that the structure of the wingtip device separates away from the structure of the fixed wing along theinterfacing cut line as the wing tip device rotates away from the flightconfiguration. Put another way, consider a point P^(wt) along theinterfacing cut line, in the curved section, which lies on the wing tipdevice side, and is at a radius R1 from the axis of rotation. When thewing tip device is in the flight configuration, a corresponding pointP^(fw) on the fixed wing side of the cut line will be at substantiallythe same radius (R1) from the axis. As the wing tip device rotates awayfrom the flight configuration by an angle α, the point P^(wt) on thewing tip device will rotate about the axis. That point P^(wt) is stillat the radius R1 from the axis (because it lies on the wing tip device),but since the radius of the cut line increases as the cut line passesaround the axis, a radially outward point P^(fw) _(α) on the wing tipdevice (that is at the same angular location a around the axis as thenew position of P^(wt)) will be at a greater radius (R2) from the axisdue to the behaviour of the curved section. The wing tip device andfixed wing will therefore necessarily move apart along the interface asthe wing tip device moves away from the flight configuration (and viceversa they will move towards each other when moving into the flightconfiguration). Such movement is beneficial because it tend to avoidrelative sliding movement at the interface.

The radius of the curved section preferably increases as the cut linepasses around the axis in a direction such that the fixed wing and thewing tip device separate along the interface as the as the wing tipdevice moves from the flight configuration to the ground configuration.The radius of the curved section preferably increases as the cut linepasses around the axis in a direction of rotation that moves the wingtip device from the flight configuration to the ground configuration.Correspondingly, the radius of the curved section preferably constantlydecreases as the cut line passes around the axis in the direction ofrotation that moves the wing tip device from the ground configuration tothe flight configuration.

The above-mentioned directions are to be considered from a view alongthe axis of rotation, towards the surface of the wing on which theinterfacing cut line lies. For example, in embodiments on which thecurved section of the interfacing cut line is located on the uppersurface of the wing, the directions are considered from a view along theaxis of rotation onto that upper surface. In general, unless otherwisespecified, it will be appreciated that references to the shape, radiusor other features of the interfacing cut line are to be taken whenviewing the cut line in this direction along the axis of rotation, andonto the surface of the wing on which the relevant part of theinterfacing cut line lies. In other words the features of the curvedsection may be considered with reference to a projection of the curvedsection onto a plane that is perpendicular to the axis of rotation.

The wing tip device (preferably the tip of that wing tip device) may beconfigured to rotate generally upwards and rearwards when moving fromthe flight configuration to the ground configuration. Thus, the radiusof the curved section is preferably arranged to increase as the curvedsection of the cut line passes around the axis from a rearward locationon the wing, towards a forward location on the wing.

In principle, embodiments of the invention may comprise a curved sectionthat follows any shape, so long as the radius of that curved sectioncontinuously increases as the cut line passes around the axis. Morepreferably, the curved section substantially follows a spiral centred onthe axis of rotation. A spiral has been found to be an especiallyeffective way of achieving the required behaviour of the change inradius.

The wing may comprise an upper surface extending from the leading edge,over the wing, to the trailing edge, and the wing may comprise a lowersurface extending from the leading edge, under the wing, to the trailingedge. The curved section may be on the upper surface of the wing.

The curved section is preferably only a proportion of the entire lengthof the interfacing cut line. The interfacing cut line may furthercomprise a first length extending rearwardly from the curved section anda second length extending forwardly from the curved section. The firstand second lengths preferably do not form respective curved sectionsthat have a radius which increases as the cut line passes around theaxis of rotation. For example, the first and second lengths arepreferably not spirals centred on the axis of rotation.

The curved section may be a transition section between the first andsecond lengths.

The second length may be formed by a cut through the outer surface thatextends within a plane containing the axis of rotation, or within aplane parallel thereto. Providing a second length that is formed by acut through the outer surface that lies within a plane containing theaxis of rotation, or within a plane parallel thereto, has been found tobe especially beneficial. It has been recognised that by forming thesecond length in this manner, the orientation of the second length ofthe interfacing cut line tends to mean the fixed wing and the wing tipdevice separate (along the second length) in a locally perpendiculardirection. Thus the sealing movement tends to be a pure compression.

The second length is preferably formed by a cut through the outersurface that lies within a plane containing the axis of rotation.Providing a cut in this orientation, may enable the fixed wing and wingtip device to separate simultaneously along the full length of thesecond cut line, as the wing tip device moves from the flightconfiguration towards the ground configuration.

The present invention has been found to be especially beneficial onarrangements in which the wing tip device is generally rotatable in themanner described in WO2015/150835. Accordingly, the wing tip device andthe fixed wing may be separated along a notional primary cut plane, theaxis of rotation being orientated normal to the primary cut plane. Theprimary cut plane may be obliquely orientated.

In embodiments having first and second lengths of the interfacing cutline (extending either side of the curved section), the first length maybe formed by a cut that is offset from the primary cut plane in a firstdirection. In some embodiments, the second length, may be offset fromthe primary cut plane in a second opposite direction. In more preferableembodiments, the second length may be formed by a cut through the outersurface that lies within a plane containing the axis of rotation.

In embodiments in which the wing tip device is rotatable in this manner,it has been found that separating the interfacing cut line into thefirst and second lengths, either side of the curved section has beenfound to be beneficial. More particularly, since the first and secondlengths are not within the primary cut plane, when the wing tip devicerotates about its axis of rotation there tends to be limited, or no,sliding contact movement along these lengths. Instead, the fixed wingand the wing tip device tend to separate (along the first and secondlengths) under a local translational movement. This is beneficialbecause it may enable a non-sliding seal (for example a compressionseal) to be employed along these lengths. In all embodiments, theorientation of the axis is preferably such that when the wing tip deviceis rotated about the axis, from the flight configuration to the groundconfiguration, the span of the aircraft wing is reduced.

In embodiments comprising a primary cut plane, the primary cut planepreferably extends through the upper and lower surfaces of the wing. Thedistance, along the upper surface of the wing, from the root of the wingto the cut plane (i.e. to where the cut plane intersects the uppersurface) may be less than the distance, along the lower surface of thewing, from the root of the wing to the cut plane (i.e. to where the cutplane intersects the lower surface). Thus, the cut plane may create anovercut with respect to the fixed wing. In other embodiments, thedistance, along the upper surface of the wing, from the root of the wingto the cut plane (i.e. to where the cut plane intersects the uppersurface) may be more than the distance, along the lower surface of thewing, from the root of the wing to the cut plane (i.e. to where the cutplane intersects the lower surface). Thus, the cut plane may create anundercut with respect to the fixed wing.

The primary cut plane is preferably a notional plane separating thefixed wing and the wing tip device (for example a cut plane createdduring the design phase of the wing). It will be appreciated that thecut plane need not necessarily manifest itself as a physical, planar,surface throughout the depth of the wing. The primary cut plane will bereadily identifiable to the skilled person. The primary cut plane may beplane within which the wing tip device rotates. Some embodiments of theinvention may comprise a bearing, such as a slew ring, for supportingrotation of the wing tip device. The bearing may be co-axial with therotational axis. The primary cut plane may extend through the thicknessof the bearing, and typically through the mid-thickness of the bearing(i.e. the mid-thickness of the bearing is co-planar with the primary cutplane).

The axis of rotation may be orientated at an angle to (i.e. notincluding being parallel or perpendicular to a longitudinal direction.The axis is preferably at an angle to (i.e. not including being parallelor perpendicular to a lateral direction. The axis is preferably at anangle to (i.e. not including being parallel or perpendicular to avertical direction. The vertical, longitudinal and lateral directionsmay be mutually perpendicular. In some embodiments, the longitudinal,lateral and vertical directions may be in an absolute frame of reference(i.e. longitudinal is fore-aft, lateral is port-starboard and verticalis vertical from the ground). The longitudinal direction may be achordwise direction; the lateral direction may be a spanwise direction.In other embodiments, it may be appropriate to use the longitudinal,lateral and vertical directions in a frame of reference local to thewing. For example, for a swept wing the longitudinal direction mayinstead be along the length of the wing, and the lateral direction maybe along the width of the wing (i.e. from the leading to the trailingedges, measured perpendicular to the longitudinal direction).Alternatively or additionally, for a wing with dihedral, the verticaldirection may be perpendicular to the plane of the wing. In all cases,the cut plane/axis is orientated such that the span of the wing isreduced when the wing tip device is rotated about the axis.

The wing tip device is preferably rotatable about a single axis ofrotation. For example, the rotation of the wing tip device is preferablynot the result of a compound rotation (I.e. a net rotation created by aplurality of separate rotations about separate axes).

The axis is preferably at an angle of less than 45 degrees, and morepreferably less than 25 degrees, from the vertical. The axis may be atan angle of 15 degrees from the vertical axis. The present invention hasbeen found to be especially beneficial in embodiments in which the axisis at a relatively small angle from the vertical because the orientationof axis results in a shallow cut plane and the area of the interfacebetween the fixed wing and wing tip device may therefore be relativelylarge.

Embodiments of the present invention have been found to be especiallybeneficial when there is a desire to create a seal between the fixedwing and the wing tip device. The wing may comprise a sealing assemblyfor sealing between the fixed wing and the wing tip device when the wingtip device is in the flight configuration. The wing may comprise anupper surface extending from the leading edge, over the wing, to thetrailing edge. The wing may comprise a lower surface extending from theleading edge, under the wing, to the trailing edge. The curved sectionmay be along the upper surface of the wing. The curved section may bealong the lower surface of the wing. The interfacing cut line maycomprise the curved section along the upper surface and a second curvedsection along the lower surface. The second curved section maysubstantially correspond to the shape of the first curved section(namely the second curved section may be centred on the axis ofrotation, the radius of the second curved section constantly increasingas the cut line passes around the axis). Features described withreference to the (first) curved section may be equally applicable to thesecond curved section.

The interfacing cut line extends all the way around the wing. Inembodiments in which the interfacing cut line comprises first curvedsection on the upper surface, first and second lengths of theinterfacing cut line either side of that curved section, and a secondcurved section on the lower surface, the interfacing cut line mayfurther comprise a third length, on the lower surface of the wing. Thethird length may be formed by cut through the outer surface of the wingbut offset from the primary cut plane. The offset may be in a seconddirection, opposite to the first direction (i.e. in an oppositedirection of offset to the first length). The second curved section maybe a transition section over which the interfacing cut line transitionsfrom the third length to the part of the second length on the lowersurface.

In embodiments comprising first and second lengths of the interfacingcut line: the first length is preferably located aft of the axis ofrotation; the second length is preferably located fore of the axis ofrotation. In embodiments further comprising a third length, the thirdlength may be located aft of the axis of rotation. In embodiments of thepresent invention, the wing tip device is configurable between: (a) aflight configuration for use during flight and (b) a groundconfiguration for use during ground-based operations, in which groundconfiguration the wing tip device is moved away from the flightconfiguration such that the span of the aircraft wing is reduced. In theflight configuration, the span may exceed an airport compatibilitylimit. In the ground configuration the span may be reduced such that thespan (with the wing tip device in the ground configuration) is lessthan, or substantially equal to, the airport compatibility limit. Theairport compatibility limit is a span limit (for example relating toclearance restrictions for buildings, signs, other aircraft). Thecompatibility limit is preferably a gate limit.

The wing tip device may be a wing tip extension; for example the wingtip device may be a planar tip extension. In other embodiments, the wingtip device may comprise, or consist of, a non-planar device, such as awinglet.

In the flight configuration the trailing edge of the wing tip device ispreferably a continuation of the trailing edge of the fixed wing. Theleading edge of the wing tip device is preferably a continuation of theleading edge of the fixed wing. There is preferably a smooth transitionfrom the fixed wing to the wing tip device. It will be appreciated thatthere may be a smooth transition, even where there are changes in sweepor twist at the junction between the fixed wing and wing tip device.However, there are preferably no discontinuities at the junction betweenthe fixed wing and wing tip device. The upper and the lower surfaces ofthe wing tip device may be continuations of the upper and lower surfacesof the fixed wing. The span ratio of the fixed wing relative to the wingtip device may be such that the fixed wing comprises 70%, 80%, 90%, ormore, of the overall span of the aircraft wing.

When the wing tip device is in the ground configuration, the aircraftincorporating the wing, may be unsuitable for flight. For example, thewing tip device may be aerodynamically and/or structurally unsuitablefor flight in the ground configuration. The aircraft is preferablyconfigured such that, during flight, the wing tip device is not moveableto the ground configuration. The aircraft may comprise a sensor forsensing when the aircraft is in flight. When the sensor senses that theaircraft is in flight, a control system is preferably arranged todisable the possibility of moving the wing tip device to the groundconfiguration.

The aircraft is preferably a passenger aircraft. The passenger aircraftpreferably comprises a passenger cabin comprising a plurality of rowsand columns of seat units for accommodating a multiplicity ofpassengers. The aircraft may have a capacity of at least 20, morepreferably at least 50 passengers, and more preferably more than 50passengers. The aircraft is preferably a powered aircraft. The aircraftpreferably comprises an engine for propelling the aircraft. The aircraftmay comprise wing-mounted, and preferably underwing, engines.

According to another aspect of the invention, there is provided anaircraft wing for use as the wing in the aircraft of another aspect ofthe invention. The wing may have a fixed wing with a wing tip devicemoveably mounted at the outer end thereof, the wing tip device beingmoveable between: (a) a flight configuration for use during flight; and(b) a ground configuration for use during ground-based operations, inwhich ground configuration the wing tip device is rotated away from theflight configuration about an axis of rotation such that the span of theaircraft wing is reduced. When the wing tip device is in the flightconfiguration, the outer end of the fixed wing and the inner end of thewing tip device meet along an interfacing cut line that separates theouter surfaces of the fixed wing and the wing tip device. Theinterfacing cut line comprises: a curved section centred on the axis ofrotation, the radius of the curved section continuously increasing asthe cut line passes around the axis.

According to another aspect of the invention, there is provided a fixedwing, for use as the fixed wing in other aspects of the inventiondescribed herein. The fixed wing is preferably configured to receive awing tip device that is rotatable, about an axis of rotation. The outerend of the fixed wing is shaped such that it would meet the inner end ofthe wing tip device meet along an interfacing cut line that separatesthe outer surfaces of the fixed wing and the wing tip device, theinterfacing cut line comprising: a curved section centred on the axis ofrotation, the radius of the curved section continuously increasing asthe cut line passes around the axis.

According to another aspect of the invention, there is provided a wingtip device, for use as the wing tip device in other aspects of theinvention described herein. The wing tip device is configured to bereceived on a fixed wing, such that the wing tip device may be rotatablebetween the flight and ground configurations, about an axis of rotation.The inner end of the wing tip device is shaped such that it would meetthe outer end of the fixed wing along an interfacing cut line thatseparates the outer surfaces of the fixed wing and the wing tip device,the interfacing cut line comprising: a curved section centred on theaxis of rotation, the radius of the curved section continuouslyincreasing as the cut line passes around the axis.

According to another aspect of the invention, there is provided a methodof designing an interface between the outer end of a fixed wing and theinner end of a wing tip device for an aircraft, the wing tip devicebeing moveable between: (i) a flight configuration for use duringflight; and (ii) a ground configuration for use during ground-basedoperations, in which ground configuration the wing tip device is rotatedaway from the flight configuration about an axis of rotation such thatthe span of the aircraft wing is reduced, wherein the method comprisesthe steps of: defining an interfacing cut line that separates the outersurfaces of the fixed wing and the wing tip device, by defining a curvedsection centred on the axis of rotation, the radius of the curvedsection continuously increasing as the cut line passes around the axis.The method may comprise a step in which the wing tip device is thenmanufactured to that design.

According to yet another aspect of the invention, there is provided anaircraft comprising a wing, the wing having a fixed wing with a wing tipdevice moveably mounted at the outer end thereof, the wing tip devicebeing moveable between: (a) a flight configuration for use duringflight; and (b) a ground configuration for use during ground-basedoperations, in which ground configuration the wing tip device is movedaway from the flight configuration such that the span of the aircraftwing is reduced. The wing tip device may be rotatable between the flightand ground configurations, about an inclined axis of rotation, such thatthe wing tip device rotates upwards and rearwards when moving from theflight to ground configurations. When the wing tip device is in theflight configuration, the outer end of the fixed wing and the inner endof the wing tip device meet along an interfacing cut line that separatesthe outer surfaces of the fixed wing and the wing tip device. Theinterfacing cut line comprises a substantially spiral-shaped curvedsection centred on the axis of rotation, the radius of the curvedsection continuously increasing as the cut line passes around the axissuch that adjacent portions of the fixed wing and wing tip device eitherside of the interfacing cut line, separate as the wing tip device movesfrom the flight configuration towards the ground configuration. Theinterfacing cut line may further comprise: a leading edge sectionpassing over the upper surface, through the leading edge and onto thelower surface, the leading edge section of the cut line being formed bya cut that extends within a plane containing the axis of rotation. Theinterfacing cut line may comprise an upper surface section located onthe upper surface and to the rear of the axis of rotation and beingoffset inboard from the plane containing the axis of rotation. Theinterfacing cut line may comprise a lower surface section located on thelower surface to the rear of the axis of rotation and being offsetoutboard from the plane containing the axis of rotation. The leadingedge section and the upper surface section may be linked by the curvedsection, and the other end of the leading edge section and the lowersurface section may be linked by a further curved section, the furthercurved section also being substantially spiral-shaped centred on theaxis of rotation, the radius continuously increasing as the cut linepasses around the axis such that adjacent portions of the fixed wing andwing tip device either side of the interfacing cut line, separate as thewing tip device moves from the flight configuration towards the groundconfiguration.

It will be appreciated that any features described with reference to oneaspect of the invention are equally applicable to any other aspect ofthe invention, and vice versa. For example features described withreference to the aircraft of the first aspect may also be applicable tothe wing, wing tip device and/or methods of the other aspects of theinvention, and vice versa.

The term ‘or’ shall be interpreted as ‘and/or’ unless the contextrequires otherwise.

DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying schematic drawings ofwhich:

FIGS. 1a and 1b show a wing with a moveable wing tip device of the priorart;

FIG. 2 is an above-frontal view of a suggested embodiment in unpublishedapplication GB1610108.1, showing the fixed wing/wing tip deviceinterface, the interfacing cut-lines and the cut planes;

FIG. 3a shows a simplified planform view of a wing on an aircraft of afirst embodiment of the invention, the wing being shown with the wingtip device in both the flight and ground configurations;

FIG. 3b is a frontal view of the aircraft incorporating the wing of FIG.3 a;

FIG. 4 is an above-frontal view of the wing in the vicinity of the fixedwing/wing tip device interface in the first embodiment of the invention,and is taken from a similar view point to that used in FIG. 2;

FIG. 5a is another above-frontal view of the wing in the vicinity of thefixed wing/wing tip device interface, showing the interfacing cut-linesand the cut planes;

FIG. 5b is a plan view looking in a direction along the axis of rotationof the wing tip device in FIG. 5 a;

FIGS. 6a and 6b are the same as those in FIGS. 5a and 5b except that thewing tip device is in the ground configuration rather than the flightconfiguration;

FIG. 7 is a frontal view along the arrow A of FIG. 6 a;

FIG. 8 is another plan view looking in a direction along the axis ofrotation of the wing tip device;

FIGS. 9a-9c show a close up view of the transition region (circled inFIG. 8) as the wing tip device moves from the flight to the groundconfigurations; and

FIG. 10 is another plan view looking in a direction along the axis ofrotation of the wing tip device, but also showing the interfacing cutline on the lower surface of the wing.

DETAILED DESCRIPTION

FIG. 1a is a perspective view of a fixed wing 1 and a wing tip device 3on an aircraft shown in WO2015/150835. In summary, the wing tip device 3is moveable between a flight configuration (FIG. 1a ) and a groundconfiguration (FIG. 1b ). In the flight configuration, the leading andtrailing edges 5′, 7′ of the wing tip device 3 are continuations of theleading and trailing edges 5, 7 of the fixed wing 1. Furthermore, theupper and lower surfaces of the wing tip device 3 are continuations ofthe upper and lower surfaces of the fixed wing 1.

The wing tip device 3 is placed in the flight configuration for flight.In the flight configuration, the wing tip device 3 thus increases thespan of the aircraft (thereby providing beneficial aerodynamic effects,for example, reducing the component of induced drag and increasing thelift). In principle, it would be desirable to maintain this large spanat all times and simply have a large fixed wing. However, the maximumaircraft span is effectively limited by airport operating rules whichgovern various clearances required when manoeuvring around the airport(such as the span and/or ground clearance required for gate entry andsafe taxiway usage). Thus, the wing tip device 3 is moveable to a groundconfiguration for use when on the ground.

In the ground configuration (FIG. 1b ) the wing tip device 3 is folded,from the above-mentioned flight configuration, by rotating the wing tipdevice 3 about a rotational axis 11. By folding the wing tip device 3 inthis manner, the span of the aircraft 2 is reduced. When the wing tipdevice 3 is in the ground configuration, the aircraft 2 thus complieswith the above-mentioned airport clearances etc.

The movement of the wing tip devices is determined by the type of jointabout which the wing tip device rotates relative to the fixed wing. Toachieve the above-mentioned movement, the wing tip device 3 and thefixed wing 5 are separated along an oblique cut plane 13 passing throughthe upper and lower surfaces of the wing. The wing tip device 3 isrotatable about the axis 11 that extends in a direction perpendicular tothe oblique cut plane 13. The axis 11 is orientated at an acute angle toall three mutually perpendicular axes X, Y and Z (i.e. chordwise,spanwise and vertical).

Small gaps, steps or other mismatch at the interface between the outerend of the fixed wing and the inner end of the wing tip device, when themoveable wing tip device is in the flight configuration, can createaerodynamic penalties (e.g. drag and pressure leakage). In some moveablewing tip arrangements, such as the one described above with reference toFIGS. 1a and 1b , it has been difficult to provide an interface thateliminates these features. For example, in some arrangements,controlling the tolerances in the vicinity of the interface has beenfound to be difficult. It has also been found to be difficult to providean effective sealing arrangement to inhibit leakage flow through theinterface.

FIG. 2 is an above-frontal view of a suggested embodiment in unpublishedapplication GB1610108.1. FIG. 2 shows the wing 101 in the vicinity ofthe joint between the fixed wing 105 and wing tip device 103. The wing101 has an upper surface 131 and a lower surface 133. The fixed wing 105and the wing tip device 103 are separated along the notional primary cutplane 113 (to which the axis of rotation is perpendicular).

The primary cut plane 113 is indicated in FIG. 2 by the dashed-linewhere it intersects the wing. First and second offset, parallel, planes113 a, 113 b (see below) are also indicated in FIG. 2 by thedashed-lines where those planes intersects the wing respectively. Partsof an interfacing cut line 135 extend within those planes, and this isshown by the solid lines in FIG. 2. The outer end of the fixed wing 105and the inner end of the wing tip device 103 meet along the interfacingcut-line 135 that separates the outer surfaces of the fixed wing 105 andthe wing tip device 103. The interfacing cut-line 135 is stepped, and isformed of a series of different lengths, as will now be described:

The interfacing cut line 135 comprises a first length 137 extending fromthe trailing edge, over the upper-aft quadrant (UA) to the start of atransition section 139. The first length 137 of interfacing cut linelies in a plane 113 a that is parallel to the primary cut plane 113, butit is offset in an inboard direction.

The interfacing cut line 135 also comprises a second length 141extending from the leading edge, over the upper-fore quadrant (UF) tothe other end of the transition section 139. This second length 141 ofinterfacing cut line also lies in a plane 113 b that is parallel to theprimary cut plane 113, but it is offset in an outboard direction (i.e.in the opposite direction to the other plane 113 a).

It will be appreciated from above, that the first and second lengths137, 141 thus both lie in oblique planes parallel to the primary cutplane 113, but in planes that are offset from that primary cut plane inopposite directions.

Between the first 137 and second lengths 141 is a transition section139. The transition section 139 comprises a first section 139 a thatlies in the same plane 113 a as the first length 137 and a secondsection 139 b at which the interfacing cut jumps across from the firstplane 113 a to the second plane 113 b. The transition section 139 thustransitions the interfacing cut line 135 from the first 137 to thesecond 141 lengths.

The arrangement in FIG. 2 has been found to be beneficial, especially interms of being able to seal the interface between the wing and wing tipdevice. Nevertheless, embodiments of the present invention are thoughtto provide a yet further improvement, as will become apparent withreference to FIGS. 3a to 10.

FIG. 3a shows a planform view of a wing 1001 on an aircraft 1002 of afirst embodiment of the invention (the aircraft is shown in FIG. 3b ).In FIG. 3a , the wing 1001 is shown with the wing tip device 1003 inboth the flight and ground configurations. The flight configuration isshown in shaded form, and FIG. 3a self-evidently shows the reduction inspan that occurs when the wing tip device 1003 rotates to the groundconfiguration. For the purposes of FIG. 3a the interfacing cut linebetween the fixed wing and the wing tip device is shown in simplifiedform—its actual shape is shown in the subsequent Figures, to whichfurther reference is made below.

The wing tip device 1003 of the first embodiment is, in general terms,rotatable in a similar manner to that shown in FIGS. 1a-1b and in FIG.2. In other words, the wing tip device 1003 is rotatable about an axis1011 that is orientated normal to a notional primary oblique cut plane1013 (see FIG. 4) separating the outer end of the fixed wing 1005 andthe inner end of the wing tip device 1003. The axis 1011 is at an acuteangle to all three mutually perpendicular axes X, Y and Z (i.e.chordwise, spanwise and vertical). The wing comprises a ring-shapedslew-bearing (not shown) for guiding rotation and reacting loads intothe fixed wing. The notional primary cut plane 1013 passes through themiddle of this slew-bearing.

As evident in FIG. 7 and when comparing FIGS. 5a and 6a , the nature ofthe movement is such that as the wing tip device 1003 is rotated aboutthe axis 1011, the upper and lower surfaces of the wing tip device thatare fore of the axis 1011, move downwards; whereas the upper and lowersurface that are aft of the axis move upwards.

Aspects of the present invention particularly reside in the shape of theinterfacing cut line between the fixed wing and the wing tip device andthat will now be described in more detail with reference to FIGS. 4 to10:

Referring first to FIGS. 4, 5 a and 5 b, these show views of the regionaround the fixed wing/wing tip device interface. The wing tip device1003 is a planar wing tip extension (the distal end of which is notvisible in these Figures). In a similar manner to FIG. 2, the wing 1001has an upper surface 1031 and a lower surface 1033. The outer end of thefixed wing 1005 and the inner end of the wing tip device 1003 meet alongthe interfacing cut-line 1035 that separates the outer surfaces of thefixed wing 1005 and the wing tip device 1003. The interfacing cut line1035 is arranged such that when the wing tip device 1003 rotates fromthe flight configuration to the ground configuration, specific types ofrelative movement occur between the outer end of the fixed wing 1005 andthe inner end of the wing tip device 1003. The interfacing cut-line 1035is formed of a series of different lengths, which are described in moredetail below.

The fixed wing 1005 and the wing tip device 1003 are separated along thenotional primary cut plane 1013 (to which the axis of rotation isperpendicular). The primary cut plane 1013 is indicated in FIG. 4 by thedashed-line where it intersects the wing, but does not manifest itselfas a physical cut in the wing skin. Instead, and in common with thearrangement in FIG. 2, the interfacing cut line 1035 comprises a firstlength 1037 in the upper-aft quadrant that is offset from the primarycut plane 1013. However, in contrast to the arrangement in FIG. 2, thefirst length does not lie in a parallel plane; instead it is curved suchthat it does not lie within any single plane. Having the first length insuch a curved shape has been found to be beneficial in terms of theresulting relative movement between the fixed wing and the wing tipdevice along the interface (when the wing tip device rotates about theaxis). Furthermore, it may facilitate a relatively small transitionsection between the first length 1037, and a third length 1045 (on theunderside of the wing—see FIG. 10), in the region of the trailing edgebecause the ends of those lengths can be brought relatively closetogether.

The interfacing cut line 1035 also comprises a second length 1041located fore of the axis of rotation 1011. In contrast to thearrangement in FIG. 2, the second length is not offset outboard; insteadthe second length 1041 extends along the upper surface 1031 of the wing,passes through the leading edge and extends onto the lower surface 1031of the wing. The second length 1041 lies within a plane P (schematicallyindicated by a dashed line in some of the Figures) containing the axisof rotation 1011, and that plane also being substantially perpendicularto the front spar of the wing (not shown). This is best illustrated inFIGS. 5b, 6b and 7.

Providing a second length 1041 that is within a plane containing theaxis of rotation 1011 has been found to be especially beneficial. It hasbeen recognised that by forming the second length in this manner, thefixed wing 1005 and wing tip device 1003 separate simultaneously alongthe full length of the second cut line 1041, as the wing tip device 1003moves from the flight configuration towards the ground configuration.Furthermore, the orientation of the second length 1041 of theinterfacing cut line 1035 tends to mean the fixed wing 1005 and the wingtip device 1003 separate (along the second length 1041) in a locallyperpendicular direction. Thus the sealing movement tends to be a purecompression.

In other embodiments (not shown) the second length may not necessarilybe in a plane containing the axis of rotation—it may instead be in aparallel plane to that. Such an arrangement does not necessarily havethe simultaneously separation between the fixed wing and the wing tipdevice, but it does still tend to exhibit the perpendicular relativemovement between the two sides of the interfacing cut line which isbeneficial in terms of sealing.

A further advantageous feature of the first embodiment of the inventionis the shape of the transition section 1039 between the first and secondlengths 1037, 1041. In the first embodiment of the invention, thetransition section 1039 is substantially in the form of a spiral as willnow be explained with reference to FIGS. 8 and 9 a-9 c:

FIG. 8 is a view from above the wing along the axis of rotation 1011 ofthe wing tip device 1003, and towards the upper surface 1031 of the wingon which the interfacing cut line 1035 lies. Overlaid onto FIG. 8 aresome radii R1-R4 from the axis 1011 to the interfacing cut line 1035.

The radius of the curved section 1039 continually increases as the cutline 1035 passes around the axis 1011 in the direction of rotation thatmoves the wing tip device from the flight configuration to the groundconfiguration (shown by the curved arrow in FIG. 8). Accordingly, whenmoving from a rearward location adjacent the first length of cut line1037 to a forward location adjacent the second length 1141 of cut line,the radii behave such that R1<R2<R3<R4.

Providing an interfacing cut line having a curved section 1039 in whichthe radius of the curved section continuously increases around the axisof rotation 1011, has been found to be especially beneficial. Inparticular, since the radius of the curved section 1039 of theinterfacing cut line 1035 increases, and that curved section of theinterfacing cut line is centred on the rotational axis 1011 of the wingtip, it means that the structure of the wing tip device 1003 separatesaway from the structure of the fixed wing 1005 along this part of theinterfacing cut line 1039 as the wing tip device 1003 rotates away fromthe flight configuration. This is best illustrated with reference toFIGS. 9a to 9c , which are close up views of the area within the dashedcircle in FIG. 8 as the wing tip moves from the flight configuration(FIG. 9a ) to the ground configuration (FIG. 9c ).

Point P^(wt) along the interfacing cut line 1035, in the curved section1039, lies on the wing tip device 1003 side, and is at a radius R1 fromthe axis of rotation. When the wing tip device is in the flightconfiguration, a corresponding point P^(fw) on the fixed wing 1005 sideof the cut line 1039 will be at substantially the same radius (R1) fromthe axis—see FIG. 9a . As the wing tip device 1003 rotates away from theflight configuration by an angle α, the point P^(wt) on the wing tipdevice 1003 will rotate about the axis—see FIG. 9b . That point P^(wt)is still at the radius R1 from the axis 1011 (because it lies on thewing tip device 1003), but since the radius of the cut line 1039increases as the cut line 1039 passes around the axis, a radiallyoutward point P^(fw) _(α) on the wing tip device (that is at the sameangular location a around the axis as the new position of P^(wt)) willbe at a greater radius (R2) from the axis due to the behaviour of thecurved section 1039. The wing tip device 1003 and fixed wing 1005 willtherefore necessarily move apart along the interface 1039 as the wingtip device 1003 moves away from the flight configuration (and vice versathey will move towards each other when moving into the flightconfiguration). Similar behaviour continues to occur as the wing tipdevice 1003 rotates further to angle θ—see FIG. 9c . Such movement isbeneficial because it tend to avoid relative sliding movement at theinterface 1039.

In the first embodiment the curved section 1039 is created by creating aspline through several radii such that curved substantially follows aspiral. In other embodiments (not shown) it will be appreciated that thecurve may be an exact spiral or may be other shapes that display anincreasing radius around the axis of rotation.

It will be appreciated that the spiral shape of the curved section 1039is made with reference to the view from above and along the axis ofrotation (i.e. with reference to a projection of the curved section 1039onto a plane that is perpendicular to the axis of rotation 1011). Inreality, the shape of the curved section 1039 is also likely to extendout of this plane because of the curved nature of the outer surface ofthe wing. Nevertheless, aspects of the present invention recognise thatit is the curvature around the axis of rotation of the wing tip devicethat is especially important in allowing the fixed wing and wingtipdevice to separate effectively, and it is therefore the behaviour of thecurved shape from this view that is especially important.

Reference to the interfacing cut line in FIGS. 4 to 9 c has primarilybeen in relation to the interfacing cut line 1035 on the upper surface1031 of the wing. Corresponding features are also present on the lowersurface 1033 however, and in that respect reference is now made to FIG.10. FIG. 10 is a view from above the axis of rotation 1011 but showingthe part 1035′ of the interfacing cut line 1035 on the lower surface1033 in phantom.

The lower part 1035′ of the interfacing cut line comprises a thirdlength 1045 extending on the lower aft quadrant, and linking with thefirst length 1037 (on the upper surface aft quadrant) via a transition1047 at the trailing edge. The third length 1045 is curved such that itminimises the length of the transition section 1047, yet still avoids aclash (for example with the upper surface of the wing) as the wing tipdevice rotates to the ground configuration.

The interfacing cut line also comprises a second curved, substantiallyspiral, section 1039′ on the lower surface linking the third length 1045with an end of the second length 1041 on the lower surface 1033. Thesecond curved section 1039′ also has a radius that increases as the cutline passes around the axis 1011 from the rearward location at which itjoins the third length 1045 to a forward location at which it joins thesecond length 1041 on the lower surface (shown in dashed lines in FIG.10, where R1<R2<R3<R4). Accordingly, as the wing tip device rotates awayfrom the flight configuration, fixed wing and the wing tip device moveapart along this interfacing cut line 1035′ too.

Although radii R1 to R4 have been shown in FIG. 10, it will beappreciated that the radii need not necessarily be of the samemagnitude/exact behaviour as those on the upper surface spiral section1039.

Whilst the present invention has been described and illustrated withreference to particular embodiments, it will be appreciated by those ofordinary skill in the art that the invention lends itself to manydifferent variations not specifically illustrated herein. For example,in another embodiment of the invention (not shown), the axis of rotationextends vertically out of the plane of the wing and there is no notionalprimary cut plane that is obliquely orientated such that it passesthrough the upper and lower surfaces of the wing. Such a wing tip (whichrotates within the plane of the wing) may be referred to as a swing wingtip. In such an arrangement a curved section of an interfacing cut linehaving the spiral, or similar, behaviour to the embodiment describedherein may still be beneficial as it may prevent sliding contact at theinterface.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims. Moreover, it is to be understood thatsuch optional integers or features, whilst of possible benefit in someembodiments of the invention, may not be desirable, and may therefore beabsent, in other embodiments.

The invention claimed is:
 1. An aircraft comprising a wing, the winghaving a fixed wing with a wing tip device moveably mounted at the outerend thereof, the wing tip device being moveable between: (a) a flightconfiguration for use during flight; and (b) a ground configuration foruse during ground-based operations, in which ground configuration thewing tip device is moved away from the flight configuration such thatthe span of the aircraft wing is reduced, wherein the wing tip device isrotatable between the flight and ground configurations, about an axis ofrotation inclined with respect to a plane defined by spanwise andchordwise directions of the fixed wing, such that the wing tip devicerotates upwards and rearwards when moving from the flight to groundconfigurations, and wherein, when the wing tip device is in the flightconfiguration, an outer end of the fixed wing and an inner end of thewing tip device meet along an interfacing cut line that separates anouter surface of the fixed wing and an outer surface the wing tipdevice, the interfacing cut line comprising a curved section, wherein aradius of the curved section is a distance between the axis of rotationand the curved section, and the radius of the curved sectioncontinuously increases along the curved section in a direction towards aleading edge of the wing tip device such that adjacent portions of thefixed wing and wing tip device on either side of the interfacing cutline, separate as the wing tip device moves from the flightconfiguration towards the ground configuration.
 2. The aircraft wingaccording to claim 1, wherein the wing comprises an upper surfaceextending from the leading edge, over the wing, to a trailing edge, andthe wing comprises a lower surface extending from the leading edge,under the wing, to the trailing edge, and wherein the curved section ison the upper surface of the wing.
 3. The aircraft wing according toclaim 1, wherein the interfacing cut line further comprises a firstlength extending from the curved section to a trailing edge of the fixedwing, and a second length extending from the curved section to theleading edge of the fixed wing.
 4. The aircraft wing according to claim3, wherein the second length is formed by a cut through the outersurface that extends within a plane containing or parallel to the axisof rotation.
 5. The aircraft wing according to claim 1, wherein theaircraft wing is a first aircraft wing attached to a fuselage of anaircraft and the aircraft includes a second aircraft wing conforming toclaim 1 on an opposite side of the fuselage to the first aircraft wing.6. The aircraft according to claim 1, wherein the interfacing cut linefurther comprises: a leading edge section passing over the uppersurface, through the leading edge and onto the lower surface, theleading edge section of the cut line being formed by a cut that extendswithin a plane containing the axis of rotation, an upper surface sectionlocated on the upper surface and to the rear of the axis of rotation andbeing offset inboard from the plane containing the axis of rotation; andthe interfacing cut line comprising a lower surface section located onthe lower surface to the rear of the axis of rotation and being offsetoutboard from the plane containing the axis of rotation.
 7. The aircraftaccording to claim 6, wherein the leading edge section and the uppersurface section are linked by the curved section, and the other end ofthe leading edge section and the lower surface section are linked by afurther curved section, the further curved section also beingsubstantially spiral-shaped centered on the axis of rotation, the radiuscontinuously increasing as the cut line passes around the axis such thatadjacent portions of the fixed wing and wing tip device either side ofthe interfacing cut line, separate as the wing tip device moves from theflight configuration towards the ground configuration.